Peripheral driver circuit of liquid crystal electro-optical device

ABSTRACT

In a peripheral driver circuit of a liquid crystal electro-optical device is comprised of a shift register circuit arranged by a plurality of registers, and a circuit for supplying power to each register. When an input signal is entered into an nth register, a supply of power to at least a portion of registers other than the nth register is stopped. The shift register circuit is constructed of a P-channel type TFT and a resistor. The circuit for supplying the power controls the supply of power to the shift register by using the output of the shift register circuit. This circuit for supplying the power is arranged by a P-channel type TFT and a resistor. The consumption power of the circuit for supplying the power is equal to and lower than that of the shift register circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a peripheral driver circuit of a liquidcrystal electro-optical device, more specifically, to a peripheraldriver circuit of a liquid crystal electro-optical device operated underlow power consumption.

2. Description of the Related Art

The liquid crystal electro-optical device of FIG. 29, is well known inthe field, and is constructed of a pixel matrix portion 2901, a signalline driver circuit 2902, and a scanning line driver circuit 2903.

In the pixel matrix portion 2901, a scanning line 2904 and a signal line2905 are arranged in a matrix form. More specifically, in an activematrix type, a pixel thin film transistor (TFT) 2906 is arranged on across point, the gate electrode of the pixel TFT 2906 is connected tothe scanning line 2904, the source electrode thereof is connected to thesignal line 2905, and the drain electrode thereof is connected to thepixel electrode. In general, since a liquid crystal capacitor 2907defined between the pixel electrode and the counter electrode cannotobtain a large capacitance value, a retaining capacitor 2908 forretaining electric charges is arranged adjacent to the pixel electrode.

When a voltage exceeding a threshold voltage of a pixel TFT is appliedto a scanning line, thereby turning on the pixel TFT, a drain electrodeof the pixel TFT and a source electrode thereof are brought into ashort-circuit condition. Then, the voltage on the signal line is appliedto a pixel electrode so that a liquid crystal capacitor and a retainingcapacitor are charged. When the pixel TFT is turned off, the drainelectrode is under open state, and then the electric charges stored inthe liquid crystal capacitor and the retaining capacitor are held untilthe pixel TFT is subsequently turned on.

The signal line driver circuit 2902 is constructed of a shift registercircuit 2909, a buffer circuit 2910, and a sampling circuit 2911. In theshift register circuit 2909, the input signal synchronized with a videosignal is input into a terminal 2912, and is sequentially shifted inresponse to a clock pulse. The output of the shift register circuit 2909is input via the inverter type buffer circuit 2910 to the samplingcircuit 2911.

The sampling circuit 2911 is constructed of an analog switch 2913 and aretaining capacitor 2914. The analog switch 2913 is turned on/off by thebuffer circuit 2910. Under the on state, a video signal line 2915 isshort-circuited with the retaining capacitor 2914, so that electriccharges are stored in the retaining capacitor 2914. The signal line 2905is connected to the retaining capacitor 2914 to transfer the sampledvideo signal to the respective pixels.

The scanning line driver circuit 2903 is arranged by a shift register2916 and the NAND circuit inverter type buffer 2917, and sequentiallydrives the scanning lines by inputting therein the input signalsynchronized with the vertical sync (synchronization) signal and theclock synchronized with the horizontal sync signal.

As the shift register circuit, there are certain possibility that eithera clocked inverter 3001 of FIG. 30A or a transmission gate 3002 of FIG.30B may be employed.

In FIG. 31, there is shown such a case that the clocked inverterstructured shift register of FIG. 30A is realized by a CMOS circuit.

As a peripheral driver circuit of a liquid crystal electro-opticaldevice, when a shift register is constructed by using a CMOS circuit ona transparent substrate on which a pixel matrix is formed, there are thefollowing characteristic drawbacks. That is, since a P-channel type TFTand an N-channel type TFT are manufactured, a total number ofmanufacturing steps is increased. A characteristic of a P-channel typeTFT cannot be easily made coincident with that of an N-channel type TFT.An N-channel type TFT may be readily deteriorated. To the contrary, ashift register circuit with a P-channel type TFT and a register in FIG.32 does not include the above problems caused by the shift register byusing the CMOS circuit.

In the shift register circuit using the P-channel type TFT and theregister, as shown in FIG. 32, when a P-channel type TFT 3201 is turnedon, a power source 3202 is short-circuited via a register 3204 to aground 3203, so that a through current may flow and thus powerconsumption would be increased. When the resistance value of theregister 3204 is increased so as not to cause the current flow, thedischarge operation cannot be easily performed, and a charge from thepower source voltage to the ground voltage is delayed. That is, sincethe frequency characteristic is deteriorated, it is difficult toincrease the resistance value. Such high power consumption would surelycause a serious problem when the liquid crystal electro-optical deviceis utilized in various electronic devices such as portable informationdevices.

The conventional liquid crystal electro-optical device of FIG. 33includes a pixel matrix portion 3301, a signal line driver circuit 3302,and a scanning line driver circuit 3303. In the pixel matrix portion3301, the scanning line 3304 and the signal line 3305 are arranged in amatrix form. In particular, in an active matrix type, a pixel TFT 3306is arranged at a cross portion, the gate electrode of a pixel TFT 3306is connected to the scanning line 3304, the source electrode thereof isconnected to the signal line 3305, and the drain electrode thereof isconnected to the pixel electrode.

When a voltage exceeding the threshold voltage of the pixel TFT isapplied to the scanning line, the pixel TFT is turned on. In this state,the drain electrode of the pixel TFT and the source electrode thereofare brought into the short-circuit state, and the voltage on the signalline is applied to the pixel electrode, so that electric charges arestored into the liquid crystal capacitor. When the pixel TFT is turnedoff, the drain electrode is under open state, and the electric chargesstored in the liquid crystal capacitor are held until the pixel TFT issubsequently turned on.

The liquid crystal capacitor 3307 defined between the pixel electrodeand the counter electrode cannot have a large value. As a consequence,the electric charges cannot be held by the liquid crystal capacitor 3307until the pixel TFT is turned on in the next cycle, so that the voltageapplied to the liquid crystal is changed, thereby varying gradation.Therefore, the retaining capacitor 3308 for retaining the electriccharges is arranged near the pixel electrode. Accordingly, when thepixel TFT is turned on, both the liquid crystal capacitor and theretaining capacitor are charged.

The signal line driver circuit is constructed of a shift registercircuit 3401, a buffer circuit 3402, and a sampling circuit 3403 asshown in FIG. 34. In the shift register circuit, the input signalsynchronized with the video signal is input and is sequentially shiftedin response to the clock pulse. The output of the shift register circuitis input via the inverter type buffer circuit to the sampling circuit.

The sampling circuit includes an analog switch 3404 and an retainingcapacitor 3405. The analog switch is turned on/off by the buffer circuitto sample the video signal. The sampled signal is held as the electriccharges in the retaining capacitor. The signal line is connected to theretaining capacitor, and the sampled video signal is transferred viathis signal line to the respective pixels.

As the signal line driver circuit, a decoder circuit may be utilizedinstead of the shift register circuit. When the respective pixels andthe addresses are combined in one-to-one correspondence and then thevideo signal is written into the pixel, the corresponding address isinput into the signal line driver circuit, and one of these signal linesis selected by the decoder circuit. On the selected signal line, thevideo signal is sampled by the decode signal and then is held as theelectric charge in the retaining capacitor.

Further, as the signal line driver circuit, a decoder circuit and acounter circuit may be used. The clock pulse is counted by the countercircuit, and the output of the counter circuit is used as the addresssignal. In response to the address signal, the signal line is selectedby the decoder circuit to write the sampled video signal into the pixel.

FIG. 35 shows a case that the decoder circuit is used in the signal linedriver circuit. Address signal inputs 3501 are selected by a NAND gate3502, and the output of the NAND gate 3502 is used as the input of ananalog switch 3503. The video signal is sampled by the analog switch andthe sampled video signal is stored as electric charges in the retainingcapacitor 3504. Another case where a decoder circuit and a countercircuit are employed in a signal line driver circuit is shown in FIG.36. The clock pulse input 3601 is counted by a counter circuit 3602. Theoutput of the counter circuit is selected as the address signal by aNAND gate 3603, and the output of the NAND gate 3603 is input into theanalog switch 3604. The video signal is sampled by the analog switch andthe sampled video signal is held as electric charges into a retainingcapacitor 3605.

In FIG. 37, the scanning line driver circuit is constructed of a shiftregister 3701 and a NAND circuit inverter type buffer 3702. Both theinput signal synchronized with the vertical sync signal and the clocksynchronized with the horizontal sync signal are input into the scanningline driver circuit to sequentially drive the scanning line. Also, inthis scanning line driver circuit, either a decoder circuit, or acombination of a decoder circuit and a counter circuit may be usedinstead of the shift register.

As a peripheral driver circuit of a liquid crystal electro-opticaldevice, when a shift register is constructed by using a CMOS circuit ona transparent substrate on which a pixel matrix is fabricated, there arethe below-mentioned characteristic drawbacks. That is, since a P-channeltype TFT and an N-channel type TFT are manufactured, a total number ofmanufacturing steps is increased. A characteristic of a P-channel typeTFT cannot be easily made coincident with that of an N-channel type TFT.To the contrary, a peripheral circuit using either a P-channel type oneconductivity mode TFT, or an N-channel type one conductivity mode TFTwith a register does not include the above-described problems asexplained in the above-explained peripheral circuit by using the CMOScircuit.

There is shown another circuit that a P-channel type TFT and a resisterare used. In FIGS. 38A to 38C, there are a NAND circuit (gate), a NORcircuit, and an inverter circuit as a basic circuit, which mayconstitute a JK-flip-flop of FIG. 39 and further a 4-bit counter circuitof FIG. 40. The counter circuit produces the respective output signal ofa ripple carry 4005, counter bit outputs and inverted outputs 4006 inresponse to the respective input signals of a power supply (powersource) 4001, a clear 4002, a clock 4003 and an enable 4004.

In the case that the peripheral driver circuit using the P-channel typeTFT and the resister is manufactured on the transparent substrate onwhich the pixel matrix has been fabricated, in the circuit of FIG. 38,when the P-channel type TFT is turned on, the power source isshort-circuited via the resister to the ground, so that a throughcurrent may flow and thus power consumption would be increased. When theresistance value of the resister is increased so as not to cause thecurrent flow, the discharge operation cannot be easily performed, and achange from the power source voltage to the ground voltage is delayed.That is, since the frequency characteristic is deteriorated, it isdifficult to increase the resistance value. Such high power consumptionmay surely cause a serious problem when the liquid crystalelectro-optical device is used in various electronic devices such asportable information devices.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a peripheral drivercircuit of a liquid crystal electro-optical device capable of reducingconsumption power when the entire device is driven even when such ashift register circuit with high consumption power of FIG. 32 is used.

Another object of the present invention is to provide an arrangementcapable of reducing power required to drive the overall liquid crystalelectro-optical device even when such a peripheral driver circuit ofFIG. 38 is used, namely the peripheral driver circuit arranged by a thinfilm transistor (TFT) and a resistor.

To solve the above problems, according to one aspect of the presentinvention, a peripheral driver circuit of a liquid crystalelectro-optical device is comprised of a shift register circuit arrangedby a plurality of registers, and a circuit for supplying power to eachregister or each portion. When an input signal is entered into an nthregister, a supply of power to at least a portion of registers otherthan the nth register is stopped. The shift register circuit of thepresent invention is constructed of a P-channel type TFT and a resistor.The circuit for supplying the power controls the supply of power to theshift register by using the output of the shift register circuit. Thiscircuit for supplying the power is arranged by a P-channel type TFT anda resistor. The consumption power of the circuit for supplying the poweris equal to and lower than that of the shift register circuit.

According to another aspect of the present invention, a peripheraldriver circuit of a liquid crystal electro-optical device is comprisedof a shift register circuit arranged by a plurality of registers, and acircuit for supplying power to each register or each portion. When aninput signal is entered into an nth staged register, a supply of powerto the registers before an (n−2)th register and after an (n+2)thregister is stopped. The shift register circuit of the present inventionis constructed of a P-channel type TFT and a resistor. The circuit forsupplying the power controls the supply of power to the shift registerby using the output of the shift register circuit. This circuit forsupplying the power is arranged by a P-channel type TFT and a resistor.The consumption power of the circuit for supplying the power is equal toand lower than that of the shift register circuit.

According to another aspect of the present invention, a peripheraldriver circuit of a liquid crystal electro-optical device is comprisedof a shift register circuit arranged by a plurality of registers, and acircuit for supplying power to each register or each portion. When aninput signal is entered into an nth register, a supply of power to theregisters before an (n−x)th register and after an (n+y)th register isstopped (x≧2, and y≧2). The shift register circuit of the presentinvention is constructed of a P-channel type TFT and a resistor. Thecircuit for supplying the power controls the supply of power to theshift register by using the output of the shift register circuit. Thiscircuit for supplying the power is arranged by a P-channel type TFT anda resistor. The consumption power of the circuit for supplying the poweris equal to and lower than that of the shift register circuit.

According to another aspect of the present invention, a peripheraldriver circuit of a liquid crystal electro-optical device is comprisedof a shift register circuit arranged by a plurality of registers, and acircuit for supplying power to each register or each portion. In thisperipheral driver circuit, the shift register circuit is subdivided intoa plurality of blocks, each of these plural blocks is arranged by morethan one register, whereas the power supply circuit is independentlyconnected to each of these plural blocks. When an input signal isentered into a register for constituting one of plural blocks, thesupply of power to any blocks other than this block is stopped. Theshift register circuit of the present invention is constructed of aP-channel type TFT and a resistor. The circuit for supplying the poweris operated at consumption power equal to and lower than that of theshift register.

To lower the consumption power of the overall peripheral driver circuit,operation of a shift register employed in the peripheral driver circuitwill now be considered. A function required for a shift register in theperipheral driver circuit of the liquid crystal electro-optical deviceis to transfer one signal in synchronism with a clock. That is, only aportion of the peripheral driver circuit functions as a shift register.

Accordingly, in FIG. 1, when an input signal is entered into an nthregister 103 of a shift register 102 with respect to a liquid crystaldisplay portion 101, a supply of power to the registers before the(n−1)th register which have transferred the signal may be stopped orinterrupted, while maintaining such an output giving no adverseinfluence to the final stage of a buffer 104 and a sampler 105. Further,the supply of power to the registers after a (n+1)th register 107,before the input signal is transferred, may be stopped. Similarly, in ashift register 108, when the input signal is entered into the nthregister 110, the supply of power to the register 111 before the (n−1)thregister, and also to the register 112 after the (n+1)th register may bestopped, while maintaining an output giving no advance influence to abuffer 109.

As described above, although high consumption power is required when theoverall circuit is operated, overall consumption power may be suppressedby operating only the necessary circuit portion, even if the respectiveconsumption power thereof is not changed.

In FIG. 12A, there is shown the peripheral driver circuit of the liquidcrystal electro-optical device comprising a shift register circuitarranged by a plurality of registers, and a circuit for supplying powerto each register or each portion. When an input signal is entered intoan nth register, a supply of power to the registers before an (n−2)thregister and after an (n+2)th register is stopped.

In the shift register for the peripheral driver circuit of the liquidcrystal electro-optical device, when the two adjacent registerssimultaneously produce an active output, the (n−1)th register alsoproduces the active output at a time when the input signal has reachedthe nth register, so that the supply of power to the registers beforethe (n−2)th resister may be stopped.

When a pulse width is surely defined by one time period of the clock,the supply of power to the (n+1)th register which needs not produce theactive output when the input signal reaches the nth register is started,and then the input signal is surely transferred at the next clockchange. As a consequence, when the input signal reaches the nthregister, the supply of power to the registers after the (n+2)thregister may be stopped. When it is allowable in any changes of thepulse width of the input signal caused by the element delay, the supplyof power to the registers after (n+1)th register may be stopped.

In FIG. 18A, when a total element number is desirably reduced ratherthan a reduction of consumption power, stopping of the power supply isnot limited to the above case, i.e., the power supply to the registersbefore the (n−2)th register and after the (n+2)th register is stopped.That is, when the input signal reaches the nth register, the supply ofpower to the (n−x)th registers (x≧2) may be stopped because the powersupplying operation to the (n−2)th register is continued, and no powersupplying operation to the (n−3)th nor (n−4)th registers is carried out.

When the input signal reaches the nth register, the power supplyingoperation to the (n+y)th register (y≧2) may be stopped, because thepower is supplied to the (n+2)th register and no power supplyingoperation to the (n+3)th and (n+4)th registers is carried out.

In FIG. 4, there is shown the peripheral driver circuit of the liquidcrystal electro-optical device comprising a shift register circuitarranged by a plurality of registers, and a circuit for supplying powerto each register or each portion. The shift register circuit has aplurality of blocks. Each block is constructed by at least two register.The power supply circuits are connected with each block independently.When an input signal is entered to a register included in one of theblocks, the power supply to blocks other than the one block is stopped.

The power supply circuit is shown in FIG. 8. It is possible that thecontrol circuit is provided with each of these registers, to control asingle register. When the control circuit becomes complex, it ispreferable that several registers are combined with each other toconstruct one block for control. In this state, the power supply voltageis applied to two blocks during such a time period when the input signalis transmitted/received between these blocks. The power supply voltageis applied to one block for receiving the input signal, whereas thesupply of power to the other block for receiving no input signal may bestopped.

Further, a peripheral driver circuit of a liquid crystal electro-opticaldevice is arranged by one conductivity type TFT and a capacitor.Alternatively, a peripheral driver circuit of a liquid crystalelectro-optical device includes a circuit for controlling a power supplyoperation, which is constructed of one conductivity type TFT, a resistorand a capacitor.

According to one aspect of the present invention in the peripheraldriver circuit of the liquid crystal electro-optical device, when thepower is supplied to the circuit portion required to specify the pixel,the power supply operation to at least a portion of the above circuitportion is interrupted.

According to another aspect of the present invention in the peripheraldriver circuit of the liquid crystal electro-optical device, when thepower is supplied to the circuit portion required to specify the pixel,the power supply voltage applied to at least a portion of the abovecircuit portion is lowered.

Also, according to another aspect of the present invention, in thescanning line driver circuit of the peripheral driver circuit of theliquid crystal electro-optical device, when either the voltage isapplied to the nth pixel, or the sampling signal is sampled by the nthsampling circuit in the signal line driver circuit, the power supplyvoltage is lowered which is applied to the portions corresponding to thepixels after the (n+1)th pixel, and the portions corresponding to thepixels before the (n−2)th pixel.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when eitherthe voltage is applied to the nth pixel, or the sampled video signal iswritten into the nth pixel, the power supply voltage is reduced which isapplied to the portion corresponding to (n+x)th pixel (x≧1) and theportion corresponding to (n−y)th pixel (y≧2) in the peripheral drivercircuit.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix arrangement are subdivided into aplurality of blocks, and there is neither such a pixel to which thevoltage is applied, nor such a pixel into which the sampled video signalis written, the power supply operation to at least a portioncorresponding to the pixel in the block is stopped.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix structure are subdivided into aplurality of blocks and there is either a pixel to which the voltage isapplied in the nth block among the plural blocks, or a pixel into whichthe sampled video signal is written, the power supply operation to theperipheral driver circuit corresponding to the pixel of at least aportion of the blocks after the (N+1)th block and before the (n−1)thblock is stopped.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix structure are subdivided into aplurality of blocks and there is either a pixel to which the voltage isapplied in the nth block among the plural blocks, or a pixel into whichthe sampled video signal is written, the power supply operation to theperipheral driver circuit corresponding to the pixel of at least aportion of the (n+x)th block and the (n−y)th block (x≧1 and y≧1).

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix arrangement are subdivided into aplurality of blocks, and there is neither such a pixel to which thevoltage is applied, nor such a pixel into which the sampled video signalis written, the power supply operation to at least a portioncorresponding to the pixel in the block is lowered.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix structure are subdivided into aplurality of blocks and there is either a pixel to which the voltage isapplied in the nth block among the plural blocks, or a pixel into whichthe sampled video signal is written, the power supply operation to theperipheral driver circuit corresponding to the pixel of at least aportion of the blocks after the (n+1)th block and before the (n−1)thblock is lowered.

In the peripheral driver circuit of the liquid crystal electro-opticaldevice according to another aspect of the present invention, when aplurality of pixels having the matrix structure are subdivided into aplurality of blocks and there is either a pixel to which the voltage isapplied in the nth block among the plural blocks, or a pixel into whichthe sampled video signal is written, the power supply operation to theperipheral driver circuit corresponding to the pixel of at least aportion of the blocks after the (n+1)th block and before the (n−1)thblock is lowered.

To reduce consumption power in the peripheral driver circuit of theliquid crystal electro-optical device, the peripheral driver circuitwill now be considered. A voltage difference about 5 V is required todrive a liquid crystal in view of a transmittance-to-voltagecharacteristic. While a DC voltage is applied to a liquid crystal, theliquid crystal would be deteriorated. As a consequence, when the liquidcrystal is driven by an AC voltage, a voltage difference requiresapproximately 10 V, so that the power supply voltage of the peripheraldriver circuit requires 20 V or more.

In the point sequential scanning operation, since a video signal iswritten into a certain pixel, the peripheral driver circuit samples thevideo signal to turn on a pixel TFT. That is, the overall peripheraldriver circuit is operated so as to specify one pixel. It should benoted in the following specification that both of the below-mentionedoperations will be referred as “a pixel being specified”. That is, avideo signal is sampled with respect to a pixel by the signal linedriver circuit to charge a retaining capacitor, and/or a pixel TFTconnected to a scanning line is brought into an on state by the scanningline driver circuit.

As a consequence, even when the power is supplied to the entireperipheral driver circuit, only a portion thereof is operable.Therefore, as to the non-functional (not operated) circuit portion,namely the portion not for specifying the pixel of the peripheral drivercircuit, the power supply voltage may be reduced, or the power supplymay be stopped so as to prevent erroneous operation thereof.

In the portion not for specifying the pixel in the peripheral drivercircuit, the power supply voltage is lowered at or below 20 V to reduceconsumption power. Thus, minimum consumption power is realized.Normally, while the peripheral driver circuit is operated under voltagesequal to or lower than 20 V, the power supply voltage is set to 20 Vonly when the pixel is specified, resulting in low consumption power.

As described above, when the overall circuit is operated, high power isconsumed. However, since the high power supply voltage is applied onlyto the required portion, the overall consumption power can be suppressedeven when the respective consumption powers do not change.

Concretely speaking, in the circuit of FIG. 34, it is assumed that acircuit for firstly specifying a pixel in response to an input signal isa first circuit, and a circuit for finally specifying a pixel is an m-thcircuit. When the input signal reaches an nth circuit, an output of thenth circuit becomes active. In the circuit of FIG. 34, an output of an(n−1)th circuit also becomes active. As a result, since outputs of othercircuits become not active, the power supply voltage can be reduced.That is, the power supply voltage to the (n−2)th, (n−3)th, . . . circuitportions may be reduced. Also, the power supply voltage to the (n+1)th,(n+2)th, . . . , circuit portions may be lowered. It should be notedthat while the power supply voltage to the (n−2)th circuit portionremains, the power supply voltage to the (n−3)th, (n−4)th, . . . circuitportions may be reduced. Also, while the power supply voltage to the(n+1)th circuit portion is not charged, the power supply voltage to the(n+2)th, (n+3)th, . . . circuit portions may be reduced.

Further, several pixels are combined with each other to constitute oneblock, and the power supply may be controlled for the respective blocks.A block for firstly specifying a pixel is referred to a first block, andthe subsequent blocks are sequentially numbered. When the circuit forspecifying the pixel is present in the nth block, the power supplyoperation to the (n+1)th, (n+2)th, . . . , blocks may be stopped, or thepower supply voltage thereof may be reduced. Alternatively, while thepower supply of the (n+1)th block is not changed, the power supplyoperation to the (n+2)th, (n+3)th, . . . , blocks may be stopped, or thepower supply voltage thereof may be lowered. Alternatively, while thepower supply of the (n−1)th block is not charged, the power supplyoperation to the (n−2)th, (n−3)th, . . . , blocks may be stopped, or thepower supply voltage thereof may be lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a peripheral driver circuit constructedof a shift register circuit, and a display matrix portion;

FIG. 2 schematically shows a shift register arranged by a clockedinverter in the peripheral driver circuit;

FIG. 3 is a timing chart for showing operations of the shift register ofFIG. 2;

FIG. 4 schematically indicates a circuit arrangement according to anembodiment 1;

FIG. 5 schematically illustrates a block diagram of the embodiment 1;

FIG. 6 is a timing chart of the embodiment 1;

FIG. 7 is a decoder portion of the embodiment 1;

FIG. 8 is a power supply circuit of the embodiment 1;

FIG. 9 is a clear circuit of the embodiment 1;

FIG. 10 is a clock supply circuit of the embodiment 1;

FIG. 11 schematically shows a circuit arrangement according to anembodiment 2;

FIG. 12 is a block diagram for showing the embodiment 2;

FIG. 13 is a timing chart for indicating operations of the embodiment 2;

FIG. 14 is a control circuit of the embodiment 2;

FIG. 15 schematically indicates one register and one buffer in theembodiment 2;

FIG. 16 is a timing chart for showing operations of an embodiment 3 ofthe present invention;

FIG. 17 schematically indicates one register, a circuit for selectingclocks with respect to the one register, and a one buffer, according tothe embodiment 3;

FIG. 18 schematically indicates a block diagram of an embodiment 4;

FIG. 19 is a timing chart for indicating operations of the embodiment 4;

FIG. 20 is a one register, a control circuit for the one register, and aone buffer, according to the embodiment 4;

FIG. 21 is a shift register constructed of one conductivity type TFTsaccording to an embodiment 5;

FIG. 22 is a timing chart for showing operations of a shift register ofthe embodiment 5;

FIG. 23 schematically indicates a power supply voltage switching circuitof the shift register constructed of the one conductivity type TFTsaccording to the embodiment 5;

FIG. 24 schematically shows a power supply voltage switching controlcircuit of the embodiment 5;

FIG. 25 is a counter and a decoder, which are divided according to anembodiment 6;

FIG. 26 schematically shows a power supply stopping type counter and acontrol circuit of the embodiment 6;

FIG. 27 is a timing chart for showing operations of the counter circuitof the embodiment 6;

FIG. 28 schematically indicates a power supply voltage lowering typecounter and a control circuit according to an embodiment 7;

FIG. 29 schematically represents the conventional peripheral drivercircuit and display matrix portion for the liquid crystalelectro-optical device;

FIG. 30 schematically indicates the clocked inverter structured shiftregister and the transmission gate structured shift register;

FIG. 31 schematically shows the clocked inverter structured shiftregister of the CMOS circuit;

FIG. 32 schematically indicates the shift register constructed of theP-channel type TFT and the register;

FIG. 33 schematically shows the conventional peripheral driver circuitand pixel matrix portion;

FIG. 34 schematically shows the signal line driver circuit using theshift register;

FIG. 35 schematically indicates the signal line driver circuit using theaddress decoder;

FIG. 36 schematically represents the signal line driver circuit usingthe counter and the address decoder;

FIG. 37 schematically shows the scanning line driver circuit with usingthe shift register;

FIG. 38 schematically illustrates the basic gate arrangement constructedof the one conductivity type TFT;

FIG. 39 schematically shows the arrangement of the J/K flip-flop; and

FIG. 40 schematically indicates the arrangement of the 4-bit counter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In embodiments 1 to 4 of the present invention, shift registers with acircuit of FIG. 2 are used in which output signals from the respectiveregisters are represented in a timing chart of FIG. 3.

Embodiment 1

In the embodiment 1, a shift register is formed as blocks, and power issupplied to the respective blocks. In FIG. 4, several registers of ashift register 401 are employed to form blocks 402, 403 and 404. From acontrol circuit 405, control signals 406, 407 and 408 are supplied tothe respective blocks. The block 402 and the like will be referred to asa “shift register block” hereinafter.

When an input signal 409 to be shifted is present in a shift registerblock 404, a control signal 408 used to supply power is input into theshift register block 404. Signals 406 and 407 used to stop (interrupt) asupply of power to the blocks are input to both of the shift registerblock 402 after the shifting input signal has been transferred, and theshift register block 403 before the shifting input signal is transferredin order to stop the supply of power, so that consumption power isreduced.

In FIG. 5, there is shown such a case that eight registers are used toconstruct a single block. Although it is possible to detect an inputsignal to produce a control signal, the synchronization establishedbetween a control circuit 501 and a shift register 502 is utilized toproduce such a control signal in this circuit.

A signal from a clock oscillator 503 is input into the shift register502 and the counter 504 of the control circuit 501. An output of thecounter 504 becomes a control signal 506 through a decoder 505. Thecontrol signal 506 is input to the shift register 502. In the embodiment1, the control circuit is constructed of a CMOS circuit outside atransparent substrate on which a pixel matrix portion has been formed.

FIG. 6 is a timing chart of the control signal 506 with respect to annth block.

Based on a clock signal 601 of the clock oscillator 503 of FIG. 5, apower supply signal 602, a clear signal 603 for initialization when thenth shift register block is activated (started), and a clock supplysignal 604 are produced as three signals, to use the control signal 506.

When eight registers are used to constitute one block, power is suppliedat a time 606 other than a time period 605 required to produce anoutput, and a clock signal is started to be supplied at a time 607. Boththe time 606 and the time 607 are not provided at the same time, but atime period 608 is provided, so that the outputs are surely produced atthe activation. After the input signal in the nth block has beentransferred to the (n+1)th block, the supply of power to the nth blockmay be stopped, or interrupted at any time. In this circuit, both thepower supply operation and the clock supply operation are stopped at atime 609.

In FIG. 7, there is shown a circuit for producing the control signal 506which is supplied to the fourth block when eight registers are employedto constitute a single block. An output of a clock oscillator

clock oscillator 503 of FIG. 5 is input to a binary counter 702. Anoutput of the binary counter 702 is detected by AND gate circuits 703,704, 705, and the detected signal is synthesized by OR gate circuits706, 707 to produce the control signal.

The AND circuit 703 selects a time period required by that the shiftregister block transfers the input signal in the internal of the block.The AND circuit 704 selects a clear period. The AND circuit 705 selectsthe clear period and a time period used to transfer the input signal. Asa consequence, when the outputs of the AND circuits 703, 704, and 705are OR-logic-operated by the OR circuit 706, a power supply signal 602is produced. Also, an output of the AND circuit 704 is inverted by aninverter 708 to obtain a clear signal 603. Outputs of the AND circuits703 and 705 are processed by the OR circuit 708 to obtain a clock supplysignal 604.

In FIG. 8, there is shown a circuit for supplying power to a shiftregister block by a P-channel type thin film transistor (TFT). A powersupply (power source) line 801 at a plus side is connected via aP-channel type TFT 802 to a shift register block 803. The power supplysignal 602 is applied to a gate electrode of the P-channel type TFT 802.

FIG. 9 is a clear circuit. A P-channel type TFT 902 which may define avalue of a storage loop of a first register (stage) 901 of the shiftregister is connected at activation. A clear signal 603 is applied to agate electrode of the P-channel type TFT 902. To define the value of theloop in order that the output of the buffer 903 is not changed beforeand after the register is activated, the drain electrode of theP-channel type TFT 902 is connected to a contact point 904 when theoutput of the buffer 903 is normally at the voltage of the power supply,and is connected to a contact point 905 when the output of the buffer903 is normally at the ground voltage.

FIG. 10 is a clock supply circuit. Clock lines 1001 and 1002 areconnected via P-channel type TFTs 1003 and 1004 to a shift registerblock 1005. A clock supply signal 604 is applied to gate electrodes ofP-channel type TFTs 1003 and 1004.

As to the shift register of this embodiment, a comparison will be madeof consumption power when this shift register is utilized as theperipheral driver circuit of the liquid crystal electro-optical device.It should be noted that consumed power at a signal resister is definedby dividing a squared value of power supply voltage for each resister bya resistance value.

Since there are three resisters in one register of the conventionaldevice of FIG. 32 and thus the power is continuously supplied to allregisters, the resultant consumed power would be increased in proportionto a total number of registers. However, in the embodiment 1, althoughthere are three resisters employed in a single register, the power iscontinuously supplied only to a portion corresponding to the eightregisters for the signal transmission and the four registers due tooverlapping of the control signal with the adjacent block, but no poweris supplied to other registers. As a result, the consumption power forthe peripheral driver circuit can be considerably reduced. Even when thetotal number of registers is increased, there is no change in theconsumption power.

As a concrete example, when a shift register having 640 registers areoperated under power supply voltage of 20 V and resistance value of 300KΩ, assuming now that probability is ½ (50%) whether the power supplyvoltage output, or the ground voltage output is produced, the resultantconsumption power could be reduced to 24 mW. To the contrary, theconsumption power in the conventional device is 1,280 mW.

Embodiment 2

In the embodiment 2, control circuits are provided with each registerand an specific signal to be externally supplied is utilized.

In FIG. 11, a control circuit 1102 is employed in each register of ashift register 1101 to detect an input signal 1103, so that a controlsignal 1104 is generated. Concretely speaking, since a pulse widthcannot be assured by power supply after an input signal has reached, theshift register is activated before a half period of a basic clock beforethe input signal is reached, and the power supply is stopped orinterrupted just after the output for one period (cycle) is set to anactive state. That is, in FIG. 12A, an output 1203 of an nth block 1202of a shift register 1201 is input to an (n+1)th control circuit and an(n+2)th control circuit 1206 in a control circuit 1204.

When the output 1203 of the nth register 1202 becomes active, the(n+1)th control circuit 1205 produces a control signal 1208 used tosupply the power to the (n+1)th register 1207. Also, when the output1203 of the nth register 1202 becomes active, the (n−2)th controlcircuit 1206 produces a control signal 1210 used to stop the powersupply to the (n−2)th register 1209.

FIG. 12B shows a signal transfer when these state changes are ended andthe next clock pulse arrives. In order that the sampler 105 of FIG. 1 isnot erroneously operated even when the supply of power to the registeris started or stopped, the output of the buffer 104 of FIG. 1 should notbe varied. As a consequence, during the period where the output of thebuffer 104 of FIG. 1 can be surely obtained and no power is supplied tothe shift register 1101 of FIG. 11, the output of the buffer is used asthe input of the next register in the embodiment 2, taking account ofsuch a fact that the signal entering in the shift register 1101 areuncertain.

Based on the above explanation, there is shown a timing chart for asingle register in FIG. 13. A power supply voltage 1304 of an nthadjustment input 1303 is produced from a basic clock 1301 and a bufferoutput 1302 of the (n−1)th register.

Although one register of the shift register is operated only for aperiod longer than one period of a basic clock by 1.5 times, since thecontrol signal is delayed from the rising time of the clock and/or thefalling time thereof, a signal having a period longer than that of thebasic clock by 2 times is produced as an input signal for the nthregister of the shift register, and a pulse width is surely set to beequal to one period of the basic clock. That is, a power supply voltage1308 of an nth adjustment input 1307 is produced from an inverted signal1305 of the basic clock and a buffer output 1306 of the (N+1)thregister. Then, both the input adjustment signals 1303 and 1307 areOR-logic-operated as active high states to produce such an adjustmentsignal 1309.

Since the buffer output signal 1302 of the (n−1)th register is delayedfrom the basic clock 1301 to be varied under this condition, an erroroperation signal is produced during the period 1310 of the adjustmentsignal 1309. In this case, the buffer output signal 1302 is masked by aclock 1311 having a period longer than that of the basic clock by 1.5times, so that the operation can be surely performed. A buffer output1312 of the nth register can be produced by these signals. a powersupply signal 1313 in the nth register causes the supply of power to bestarted at a time before a half period of the basic clock, where theinput signal has arrived, so as to avoid variations in the input signalwidth caused by the element delays.

As the control circuit, such a circuit having no logic circuit isdesirable since this control circuit can store, or hold states and mustbe operated under lower consumption power. In the embodiment 2, it ispreferably conceived to construct a circuit mainly arranged by acapacitor, because of a simple circuit arrangement, although frequencycharacteristics thereof would be deteriorated.

FIG. 14 shows a control circuit. Reference numeral 1406 is a resisterfor protecting a power supply. When a capacitor 1401 is under chargingstate, a supply of power to a register is interrupted, and a controlsignal output 1402 for supplying the power to the register is producedunder discharge state.

After the power source for the overall circuit is turned on, a P-channeltype TFT 1403 sets the control circuit to the initial condition. Thatis, before the input signal is input to the shift register, the groundvoltage signal is applied to the gate electrode of the P-channel typeTFT 1403 so as to charge the capacitor 1401.

In order to surely obtain the input signal in the nth control circuit,the nth register is activated at a time when the input signal reachesthe (n−1)th register, and then the input signal is acquired at thesubsequent clock change. Accordingly, the buffer output of the (n−1)thregister is used as the input to the gate electrode of the P-channeltype TFT 1404. As a consequence, when the buffer output of the (n−1)thregister becomes the ground voltage, the capacitor 1401 is discharged toproduce a signal for supplying power to the nth register.

Similarly, in the nth control circuit, when the input signal has reachedthe (N+2)th register, the nth register is brought into such a conditionthat no active signal is output, and thus the supply of power may bestopped or interrupted. Therefore, the buffer output of the (n+2)thregister is used as an input to the gate electrode of the P-channel typeTFT 1405. As a consequence, when the buffer output of the (n+2)thregister becomes the ground voltage, the capacitor 1401 is charged andthe supply of power to the nth register is stopped.

The nth register and the buffer are shown in FIG. 15. In a signaladjusting portion 1501, the basic clock is supplied to a gate electrodeof a P-channel type TFT 1502, a clock having a period longer than thatof the basic clock by 1.5 times for the masking is applied to a gateelectrode of a P-channel type TFT 1503, and the buffer output of the(n−1)th register is applied to a gate electrode of a P-channel type TFT1504, so that a falling portion of the buffer output of the nthregister, namely a signal 1303 of FIG. 13 is produced.

A clock produced by inverting the basic clock is supplied to a gateelectrode of a P-channel type TFT 1505, a clock having a period longerthan that of the basic clock by 1.5 times for the masking is applied toa gate electrode of a P-channel type TFT 1506, and the buffer output ofthe (N+1)th register is applied to a gate electrode of a P-channel typeTFT 1507, so that a rising portion of the nth register, namely a signal1307 of FIG. 13 is produced. As a result, an output of the signaladjusting portion 1501 becomes a signal 1309 of FIG. 13. Basically,since the P-channel type TFTs 1504 and 1507 are under off states, nocurrent may normally flow through a resister 1508, and the controlsignal is not input into the signal adjusting portion.

Conventionally, all registers of the shift register have been operated.However, according to this embodiment, the control signal is applied tothe gate electrodes of the P-channel type TFTs 1509, 1510, 1511 and thesupply of power is stopped during unnecessary periods to reduce theconsumption power in the overall shift register.

The clock having the period longer than that of the basic clock by 1.5times is applied to a gate electrode of a P-channel type TFT 1512, andthe output of the signal adjusting portion 1501 is applied to a gateelectrode of a P-channel type TFT 1513, so that a buffer input for aperiod during the storage loop is not constituted is produced.

An inversion signal of the clock having the 1.5 times longer period isapplied to a gate electrode of a P-channel type TFT 1514, and an outputof an inverter 1516 for constituting the storage loop is applied to agate electrode of a P-channel type TFT 1515.

Basically, both the P-channel type TFT 1515 and the resister 1517constitute an inverter. The storage loop may be constructed of thisinverter and another inverter arranged by the P-channel type TFT 1518and the resister 1519. A P-channel type TFT 1520 and a resister 1521constitute a buffer.

A P-channel type TFT 1522 is used to define each output of the shiftregister at the clear operation, and to prevent the charging state ofthe capacitor of the control circuit from not being ensured. When thecurrent capacitance of the P-channel type TFT is large, the P-channeltype TFTs 1509, 1510 and 1511 used to supply the power may be combinedwith each other.

In the case that the pulse width of the input signal needs not beensured, the control signal is synchronized with the basic clock and thepower may be supplied to a single register only for one period in thestructure of embodiment 2.

In the shift register of this embodiment, a comparison will be madeconsumption power when this shift register is utilized as the peripheraldriver circuit of the liquid crystal electro-optical device. Theconsumed power of a signal resister is defined by dividing a squaredvalue of power supply voltage for each resistor by a resistance value.

Since there are three resistors in one register of the conventionaldevice of FIG. 32, the power is continuously supplied to all registersand the resultant consumed power registers. However, in the peripheraldriver circuit shown in the embodiment 2, although there are threeresistors employed in one register, the power is continuously suppliedonly to the three registers, but no power is supplied to otherregisters. As a result, consumption power for the peripheral drivercircuit can be considerably reduced. Even when the total number ofregisters is increased, there is no change in consumption power.

As a concrete example, when the shift register having 640 registers isoperated under the power supply voltage of 20 V and the resistance valueof 300 KΩ, assuming that probability is ½ (50%) whether the power supplyvoltage output or the ground voltage output is produced, the resultantconsumption power could be reduced to 6 mW. To the contrary, theconsumption power in the conventional device is 1,280 mW.

Embodiment 3

In an embodiment 3, a control circuit is employed in each register. Inthe embodiment 3, a circuit for masking a clock is employed in thecircuit portion where the erroneous operation is prevented using theclock having the 1.5 times longer period in the embodiment 2. As aresult, the signal treatment and the control circuit of the embodiment 3are similar to those of the embodiment 2.

In FIG. 16, there is shown a timing chart for explaining a singleregister. In the signal adjusting portion, a power supply voltage 1604of an nth input 1603 is produced from an inverted clock 1601 of thebasic clock and a buffer output 1602 of an (n−1)th register.

As a signal to form a storage loop, a clock 1605 is desired in view oftiming. However, since an nth control signal becomes a signal 1606, thestorage loop is formed at a time 1607 just after the activation, so thatthe nth input cannot be accepted. Thus, the clock 1605 is masked by thecontrol signals 1606 and 1608, so that such a loop forming signal 1609is produced. An output 1610 of the nth buffer is formed by thesesignals.

An nth register is shown in FIG. 17. As to a signal adjusting portion1701, the basic clock is applied to a gate electrode of a P-channel typeTFT 1702, and a buffer output of the (n−1)th register is applied to agate electrode of a P-channel type TFT 1703, so that a signal is setwhen the nth register is activated (initiated).

A circuit 1704 for selecting a clock produces an output 1708 by applyingthe nth control signal to a gate electrode of a P-channel type TFT 1705,by applying the (n+1)th control signal to a gate electrode of aP-channel type TFT 1706, and by applying an inverted clock of the basicclock to a gate electrode of a P-channel type TFT 1707. The outputsignal 1708 is inverted to produce a signal for forming a storage loop.

A circuit 1709 for constructing the storage loop, and the buffer circuit1710 are identical to those of the embodiment 2. P-channel type TFTs1711, 1712, 1713, 1714 and 1715 are employed to supply the power,whereas a P-channel type TFT 1716 is used to execute the clearoperation.

In the shift register of this embodiment, a comparison will be made ofconsumption power when this shift register is utilized as the peripheraldriver circuit of the liquid crystal electro-optical device. Theconsumed power at a signal register is defined by dividing a squaredvalue of power supply voltage for each resister by a resistance value.

Since there are three resistors in one register of the conventionaldevice of FIG. 32, the power is continuously supplied to all registersand the resultant consumed power would be increased in proportion to atotal number of registers. However, in the peripheral driver circuitshown in the embodiment 3, although there are five resistors employed ina single register, the power is continuously supplied only to the threeregisters, but no power is supplied to other registers. As a result, theconsumption power for the peripheral driver circuit can be considerablyreduced. Even when the total number of registers is increased, there isno change in the consumption power.

As a concrete example, when the shift register having 640 registers areoperated under the power supply voltage of 20 V and the resistance valueof 300 KΩ, assuming that probability is ½ (50%) whether the power supplyvoltage output or the ground voltage output is produced, the resultantconsumption power could be reduced to 10 mW. To the contrary, theconsumption power in the conventional device is 1,280 mW.

Embodiment 4

In an embodiment 4, a supply of power is carried out during a periodequal to two periods of the basic clock.

In the embodiments 2 and 3, the power has been supplied for the periodlonger than that of the basic clock by 1.5 times. To the contrary, sincethis power supply operation is performed for two periods of this basicclock in the embodiment 4, the entire circuit may be simplified.

A flow of signal is shown in FIG. 18A. There is no change in structuresof a shift register 1801, a buffer 1802, and a control circuit 1803.When an output of an nth register becomes active in synchronism with theclock by an active output 1804 of an (n−1)th register, an output 1806 ofa buffer 1805 corresponding to the nth buffer is varied.

When the buffer output 1806 is input to an (N+2)th control circuit 1807and an (n−2)th control circuit 1808. When the nth buffer output becomesactive, a power supply signal 1809 is produced in the (N+2)th controlcircuit 1807, whereas a power supply stopping signal 1810 is formed inthe (n−2)th control circuit 1808. clock from the state of FIG. 18A isindicated in FIG. 18B. In the embodiment 4, the output of the nthregister is used as the input to the (n+1)th register, without using theoutput of the nth buffer.

A time chart is shown in FIG. 19. In response to a clock 1901, an inputsignal is acquired, and a clock inversion 1902 constitutes a storageloop. In response to a control signal 1903, the power is supplied onlyfor two periods of the basic clock.

An output 1904 of the nth register is indicated by a solid line. Sincethe signal is acquired for periods 1905 and 1906 in the (n+1)thregister, no longer such a signal acquisition as indicated by a dottedline 1904 is carried out. When a signal 1907 input to the buffer withrespect to the nth register is employed, no erroneous operation isperformed by a buffer output 1908.

In FIG. 20, there is shown a circuit diagram of the embodiment 4. Anoutput of an nth register 2001 is used as an input to a buffer 2002 ofthe nth register and an (n+1)th register. An output of the buffer 2002becomes an input to (n+2)th and (n−2)th control circuits 2003, therebyproducing a control signal. A shift register is so arranged thatP-channel type TFTs 2004, 2005, 2006 for supplying the power areseries-connected to the respective inverters of the shift register shownin FIG. 32. The source electrodes of the P-channel type TFTs 2007, 2008,2009 which constitute the inverter may be combined at one point, and maybe connected to the power supply via a single P-channel type TFT forcontrolling the supply of power.

The buffer circuit 2002 and the control circuit 2003 have the samearrangements as those of the embodiment 2. That is, an input to a gateelectrode of a P-channel type TFT 2011 which discharges an nth controlcircuit capacitor 2010 corresponds to an output of the (n−2)th buffer,and an input to a gate electrode of a P-channel type

charging corresponds to an output of the (n+2)th buffer. P-channel typeTFTs 2013 and 2014 are a clock synchronized analog switch, and P-channeltype TFTs 2015 and 2016 are employed to carry out the clear operation.

As to the shift register of this embodiment, a comparison will be madeof consumption power when this shift register is utilized as theperipheral driver circuit of the liquid crystal electro-optical device.The consumed power of a signal register is defined by dividing a squaredvalue of power supply voltage for each resister by a resistance value.There are three resistors in one register of the conventional device ofFIG. 32 and the power is continuously supplied to all registers.Accordingly, the resultant consumed power would be increased inproportion to a total number of registers. However, in the peripheraldriver circuit of the embodiment 4, although there are three resistorsemployed in a single register, the power is continuously supplied onlyto the four registers, but no power is supplied to other registers. As aresult, the consumption power for the peripheral driver circuit can beconsiderably reduced. Even when the total number of registers isincreased, there is no change in the consumption power.

As a concrete example, when A shift register having 640 register isoperated under the power supply voltage of 20 V and the resistance valueof 300 KΩ, assuming that probability is ½ (50%) whether the power supplyvoltage output or the ground voltage output is produced, the resultantconsumption power could be reduced to 8 mW. To the contrary, consumptionpower in the conventional device is 1,280 mW.

In the embodiments 1 to 4, according to the present invention, the poweris supplied only to the required registers so as to be operated, so thatthe consumption power in the overall peripheral driver circuit of theliquid crystal electro-optical device could be greatly reduced. Evenwhen the shift register circuit with high consumption power is employed,very low consumption power could be realized for the overall peripheraldriver circuit. An increase in the consumption power in conjunction withan increase in a total number of registers could be prevented.

In embodiments 5 to 7, there are represented such circuit arrangementsthat when a pixel is specified, a power supply voltage is set to be arequired value. This may be another circuit arrangement for lowering apower supply voltage of a circuit portion which has no function.

Embodiment 5

In an embodiment 5, a shift register circuit is employed to constitute aperipheral driver circuit, and it is assumed that the circuit isrealized by employing one conductivity type TFT, namely a P-channel typeTFT and a resistor in this case. FIG. 21 shows a shift register circuit.In this embodiment, one register (stage) 2101 of the shift registercircuit corresponds to a circuit arranged by three inverters 2102, 2103,2104, and two analog switches 2105 and 2106. A buffer 2107 causes theanalog switches to be turned on/off.

In FIG. 22, a solid line indicates a power supply voltage capable ofdriving a liquid crystal, and a dotted line shows a power supply voltagecapable of realizing low consumption power. Considering a voltagevariation range of a video signal for driving a liquid crystal, a powersupply voltage of about 20 V is needed in a buffer to operate an analogswitch. Therefore, a buffer output 2201 for turning on/off the analogswitch constructed of P-channel TFTs becomes normally the power supplyvoltage of approximately 20 V, and becomes the ground voltage atsampling. As a result, such a waveform 2202 is required as the bufferinput, which becomes normally the ground voltage, and a voltage of about20 V at sampling.

It is considerable that a shift register circuit for producing thebuffer input shifts the sampling timing as the input signal.Accordingly, when the sampling timing is produced in the shift registercircuit, namely when the input signal is present in the nth register ofthe shift register circuit, assuming that the power supply voltage withrespect to the nth register is about 20 V, the liquid crystal can bedriven via the buffer, the analog switch, and the video signal. When noinput signal is present, the power supply voltage of the shift registercircuit can be lowered within a range where the shift register circuitis not erroneously operated. Since the power supply voltage for drivingthe liquid crystal is not permanently used but the power supply voltagecan be lowered within the range where the logic is not inverted in thiscircuit arrangement, consumption power can be reduced.

FIG. 23 shows a circuit arrangement for supplying a power supply voltagecapable of driving a liquid crystal and a power supply voltage capableof realizing low consumption power to one register 2301 of a shiftregister circuit. A P-channel type TFT 2302 is brought into an on stateand also a P-channel type TFT 2303 is brought into an on state, so thata power supply voltage (high power supply voltage) capable of driving aliquid crystal and another power supply voltage (low power supplyvoltage) capable of realizing lower consumption power can be supplied.

FIG. 24 shows a circuit for controlling a power supply (power source)circuit. In FIG. 24, there are shown a control circuit corresponding toan nth register 2401 of a shift register circuit, and a method forextracting a signal for operating the control circuit.

A capacitor 2402 of the control circuit corresponding to the nthregister of a shift register circuit is operated as follows. While thecapacitor 2402 is charged to the voltage capable of driving the liquidcrystal, the power supply voltage capable of realizing low consumptionpower is applied to the nth shift register of a shift register circuit.

Conversely, while this capacitor is discharged to a voltage near theground voltage, the power supply voltage capable of driving the liquidcrystal is applied to the nth register of a shift register circuit.

The control circuit is operated as follows. The P-channel type TFT 2403is previously turned on to charge the capacitor 2402 up to such avoltage capable of driving the liquid crystal. After charging, theP-channel type TFT 2403 is turned off. In initial state, the powersupply voltage capable of realizing low consumption power is supplied.The output of the (n−1)th register 2404 of the shift register circuit isconnected via a buffer to a gate electrode of a P-channel type TFT 2405.As a consequence, when an input signal reaches the (n−1)th register ofthe shift register circuit, the capacitor is discharged to a voltagenear the ground voltage. The voltage at the capacitor becomes a powersupply voltage control signal capable of driving the liquid crystal insynchronism with the clock by the P-channel type TFT 2406. Then, thiscontrol signal becomes another power supply voltage control signalcapable of realizing low consumption power via an inverter 2407. As aresult, when the capacitor of the control circuit corresponding to thenth register of the shift register circuit is discharged, the powersupply voltage capable of driving the liquid crystal is applied to thenth register of the shift register circuit, so that the supply of powercapable of realizing low consumption power is stopped. When the powersupply voltage of the shift register becomes low, the output of theshift register may erroneously operate the control circuit with the highpower supply voltage. To avoid this, the buffer output which iscontinuously used under the power supply voltage capable of driving theliquid crystal is employed.

Also, due to time delays of the inverter, there are some possibilitythat the power supply control signal simultaneously turns on both theP-channel type TFTs 2302 and 2303, whereby the power supply isshort-circuited. Therefore, the power supply voltage control signalcapable of driving the liquid crystal is distorted by a resistor 2408 todelay that the P-channel type TFT 2302 is brought into an on state, sothat the short circuit of the power supply circuit can be avoided.

Further, an output of an (N−1)th register 2409 of the shift registercircuit is connected through a buffer to a gate electrode of a P-channeltype TFT 2410. When the input signal reaches the (n+1)th register of theshift register circuit, the capacitor is charged to such a power supplyvoltage capable of driving the liquid crystal. As a result, the powersupply voltage capable of realizing lower consumption power is appliedto the nth register of the shift register circuit, so that the supply ofpower capable of driving the liquid crystal is stopped.

With this circuit arrangement, the power supply voltage can be set to anecessary value only when the analog switch is turned on for sampling.In other case, the power supply voltage is set to such a voltage capableof realizing low consumption power, so that lower consumption power ofthe overall circuit can be realized.

With respect to the peripheral driver circuit of this embodiment, acomparison is made of consumption power. The consumed power at a signalregister is defined by dividing a squared value of power supply voltagefor each resister by a resistance value. The voltage of 20 V capable ofdriving the liquid crystal is continuously applied to the circuit shownin FIG. 40, whereas there are three resistors in one register of a shiftregister circuit and a resistance value thereof is 300 KΩ, assuming thatprobability is ½ (50%) whether the power supply voltage output or theground voltage output is produced. When the shift register circuit isarranged by 640 registers and the buffer is eliminated, the consumptionpower is 1280 mW. In this embodiment, the following results areobtained. That is, assuming that the liquid crystal drive voltage is 20V, the voltage capable of low consumption power is 5 V, four resistorsare employed in one register, and a resistance value thereof is 300 KΩ,the power supply voltage capable of driving the liquid crystal isapplied only to the two registers of the shift register circuitconstructed of 640 registers, whereas the power supply voltage capableof realizing low consumption power is applied to the remaining 638registers of the shift register circuit. Based on these assumptions, theresultant consumed power may be calculated as 111 mW. Therefore,consumption power can be lowered in this embodiment.

Embodiment 6

In the embodiment 6, there is shown a circuit arrangement for supplyingpower only to a portion for specifying a pixel and for stopping(interrupting) the supply of power to a portion not for specifying apixel. In this embodiment, such a circuit is assumed that a pixel isspecified by employing a decoder circuit and a counter circuit.

An output (containing an inverted output) of the counter circuit ispassed through the decoder circuit arranged by the gate of FIG. 38, sothat a signal for specifying a pixel, is produced. When the decodercircuit has the function of a buffer, since the consumption power isdecreased, power to the counter circuit is reduced. It is impossible toseparate the counter circuit into the portion for specifying the pixeland the portion not for specifying the pixel with the circuitarrangement of FIG. 40, so that this counter circuit is subdivided.

An address corresponding to either a signal line or a scanning line isproduced not by a single counter, but by employing a counter circuithaving a less bit number as shown in FIG. 25. A necessary number ofcounter circuits are prepared and these counter circuits aresequentially driven to produce local addresses, so that the pixel isspecified. As a consequence, the supply of power to such a countercircuit which is not required to be operated can be stopped. In thisfigure, reference numeral 2501 is a pixel matrix; 2502 is a subdividedcounter circuit; 2503 is a decoder circuit; and 2504 is a controlcircuit.

FIG. 26 represents the subdivided counter circuit, the decoder circuit,and the control circuit. When a ripple carry produces in an (n−1)thcounter circuit 2601, power is started to be supplied to an nth countercircuit 2602. When an (n+1)th counter circuit 2603 starts its countingoperation, the supply of power to the nth counter circuit is stopped.

The control circuit is identical to that of the embodiment 5, and isarranged by one conductivity type TFT for initial setting (i.e.,P-channel type TFT 2604), a P-channel type TFT 2605 for discharging acapacitor so as to start the supply of power, a P-channel type TFT 2606for charging a capacitor so as to stop the supply of power, and also acapacitor 2607 for storage purpose. An output value of the nth countercircuit becomes unstable at a time when the power is started to besupplied. As a result, the clear operation is carried out at such a timewhen a ripple carry of the (n−1)th counter circuit is produced and thepower is started to be supplied. A circuit for producing a clear signalis constructed of a P-channel type TFT 2608.

A circuit for supplying the power may be realized by that a P-channeltype TFT is series-connected between the source electrode of theP-channel type TFT in FIG. 22 and the power supply (power source)circuit and the supply of power is controlled by this P-channel typeTFT. In FIG. 26, P-channel type TFTs which are additionally connected inseries are combined and indicated as a P-channel type TFT 2609. Anenable signal to the nth counter circuit 2602 is supplied by theP-channel type TFT 2609. The supply of power to the nth counter circuitis stopped by using the output of the decoder circuit 2610 for detectingthe minimum output value of the (n+1)th counter circuit.

FIG. 27 shows a timing chart of the nth counter circuit. Immediatelyafter the power supply (power source) 2701 is turned on, a clear signal2703 of the nth counter circuit is produced by a ripple carry 2702 ofthe (n−1)th counter circuit. An output 2704 of the nth counter circuitis input into the decoder circuit to produce a decode signal 2705. Inresponse to next clock pulse when the ripple carry is output, the supplyof power to the nth counter circuit is stopped.

With respect to the peripheral driver circuit of this embodiment, acomparison is made of consumption power. The consumed power at a signalregister is defined by dividing a squared value of power supply voltagefor each resistor by a resistance value. When the address signals areproduced to 640 pixels, a 10-bit counter is required. A one bit ofcounter corresponds to one piece of a J/K flip-flop and a single J/Kflip-flop requires 10 gates, so that the number of resisters forconnecting the power supply (power source) to the ground with respect toonly the J/K flip-flop is 100. Sixteen (16) gates are additionallyrequired, and there is one resistor for connecting the power supply tothe ground with respect to one gate. As a result, there is a total of116 resistors for connecting the power supply and the ground. Aresistance value is selected to be 300 KΩ and a power supply voltage is20 V, assuming that probability is ½ (50%) whether the power supplyvoltage output or the ground voltage output is produced. The consumptionpower becomes 77 mW except for the decoder circuit having also thebuffer function.

To the contrary, the consumption power according to this embodiment isgiven as follows. Since the 4-bit counters are sequentially usedirrelevant to the number of pixels, it may be considered that the 4-bitcounters are normally operated. In other words, there are four J/Kflip-flops, and ten resistors are provided in each J/K flip-flop. Sinceeight gates are required in each J/K flip-flop, a total number ofresistors for connecting the power supply and the ground becomes 48. Thepower supply voltage is selected to be 20 V, and a resistance valuethereof is 300 KΩ, assuming that probability is ½ (50%) whether thepower supply voltage output or the ground voltage output is produced.From this assumption, the consumption power becomes 32 mW except for thedecoder circuit having the buffer function.

In the peripheral driver circuit with only the decoder circuit and thecounter circuit, when the number of either the canning lines or thesignal lines is increased, the resultant consumption power is increasedin a logarithmic manner. However, in this embodiment, the consumptionpower can be reduced in view of circuit arrangements.

Embodiment 7

In an embodiment 7, there is shown a circuit arrangement that when apixel is specified, a power supply voltage is set to a necessary value.This also corresponds to a circuit arrangement for lowering a powersupply voltage of a circuit portion which does not function. Similar tothe embodiment 6, in this embodiment, such a peripheral driver circuitis assumed that a pixel is specified by employing a decoder circuit anda counter circuit. The counter circuit has 6 bit outputs.

FIG. 28 shows a circuit arrangement. A control circuit 2801 has anarrangement similar to that of the embodiment 5. A ripple carry of an(n−1)th counter circuit 2803 is employed as a signal for starting asupply of power to an nth counter circuit 2802. An output of a decodercircuit 2805 for detecting a minimum output value of an (n+1)th countercircuit 2804 is used as a signal for stopping a supply of power to thenth-counter circuit. A signal for controlling a power supply voltagecapable of realizing low consumption power is used as an enable signalof the nth counter circuit. Under a clear state, the nth counter circuitwaits that the enable signal subsequently becomes active. As aconsequence, even when the power supply voltage is changed, the clearoperation need not be executed.

With respect to the peripheral driver circuit of this embodiment, acomparison is made of consumption power. The consumed power at a singleregister is defined by dividing a squared value of power supply voltagefor each resistor by a resistance value. When the address signals areproduced to 640 pixels, a 10-bit counter is required. A one bit of thecounter corresponds to one pixel of a J/K flip-flop, and a single J/Kflip-flop requires 10 gates, so that there are 100 pieces of resistorsfor connecting the power supply to the ground only in the J/K flip-flop.Sixteen (16) gates are additionally required, and there is one resistorfor connecting the power supply to the ground with respect to one gate.As a result, there is a total of 116 resistors for connecting the powersupply and the ground. A resistance value is selected to be 300 KΩ and apower supply voltage is 20 V, assuming that probability is ½ (50%)whether the power supply voltage output, or the ground voltage output isproduced. The consumption power becomes 77 mW except for the decodercircuit having also the buffer function.

To the contrary, the consumption power according to this embodiment isgiven as follows. Eleven (11) 6-bit counters are required with respectto 640 pixels. A voltage of 20 V capable of driving the liquid crystalis applied to one 6-bit counter, whereas a voltage of 5 V capable ofsupplying low consumption power is applied to the remaining ten 6-bitcounters. In a 6-bit counter circuit, there are six J/K flip-flops, andten resistors are provided in one J/K flip-flop. Since 12 gates arerequired in each J/K flip-flop, a total number of resistors forconnecting the power supply and the ground becomes 72. It is assumedthat a resistance value thereof is 300 KΩ, and the probability is ½(50%) whether the power supply voltage output or the ground voltageoutput is produced. From this assumption, the consumption power becomes62 mW except for the decoder circuit having the buffer function.

As previously explained in the embodiments 5 to 7, according to thecircuit arrangement of the present invention, the power is supplied onlyto the required circuit portion in the peripheral driver circuit to bedriven, so that the consumption power of the overall peripheral drivercircuit in the liquid crystal electro-optical device can be reduced.Also, the high voltage is applied to the required circuit portion of theperipheral driver circuit, and the low voltage is applied to theunnecessary circuit portion thereof, so that the consumption power ofthe overall peripheral driver circuit of the liquid crystalelectro-optical device can be reduced.

1. A semiconductor device comprising: a plurality of pixels arranged ina matrix form; a driver circuit for driving said pixels, said drivercircuit comprising: a shift register circuit having a serial-connectedplurality of registers; and a power supply circuit having a plurality ofcontrol circuits connected to each of said registers to supply power toeach of said registers; wherein when an input signal to said shiftregister circuit is held in nth register of said shift register circuit,the power supplied to registers except the nth, (n−1)th and (n+1)thregister of said shift register circuit is decreased (n is an integer).